The invention, in some embodiments, relates to the field of electrochemical cells and, more particularly but not exclusively, to membranes suitable for use as separators in electrochemical cells as well as electrochemical cells including such membranes as separators. In some embodiments, the membranes include chelators of multivalent cations.
A secondary electrochemical cell generally includes a negative electrode comprising a negative active material with a reduction potential, a positive electrode comprising a positive active material with an oxidation potential and an electrolyte that allows transport of ions between the electrodes. Electrically insulating the positive electrode from the negative electrode is a separator that is permeable to the passage of ions in the electrolyte. The sum of the reduction potential and the oxidation potential is the standard cell potential of the electrochemical cell.
A well-known type of secondary electrochemical cell is the lithium-ion secondary electrochemical cell. A typical lithium-ion secondary electrochemical cell includes a lithium-ion intercalating material (typically a carbonaceous material such as graphite or hard carbon) as the negative active material and a lithium-ion containing material (e.g., a LiCoO2) as the positive active material. During cell charging, the positive active material is oxidized, releasing lithium ions into the electrolyte (e.g., LiCoO2>Li1-xCO2+xLi++xe−) while lithium ions from the electrolyte are intercalated in the negative active material (xLi++xe−+6C>LixC6). During cell discharge, the positive active material is reduced and reintegrates lithium ions from the electrolyte while lithium ions are released from the negative active material.
In primary electrochemical cells, the negative electrode is the anode and the positive electrode is more often called a cathode.
Art relevant to the teachings herein includes Kim and Lim (Surface Modified membranes as a separator for LI batteries in Energies 2010, V3 866-885) and Jarvis et al (Use of grafted PVDF based polymers in Lithium ion batteries) in Journal of Power Sources 97-98 (2001) 664-666.